1. Field of the Invention
The present invention relates to a hard disk drive (HDD), and more particularly, to a method of improving a recording performance thereof by controlling write strength according to a flying height of a head and a computer-readable recording medium having recorded thereon a computer-readable program suitable for the method.
2. Description of the Related Art
A hard disk drive (HDD), which is a type of data storage medium, reproduces data recorded on a disk or writes data on the disk using a magnetic head.
FIG. 1 is a structure of a typical HDD 10. Referring to FIG. 1, a hard disk 20 is assembled in the HDD 10 to rotate on a base 11 of the HDD 10. The HDD 10 includes at least one magnetic head positioned over a recording/reproducing surface of the rotating hard disk 20 to read or write information by sensing or magnetizing a magnetic field formed on the hard disk 20.
The magnetic head is combined with one end of a magnetic head assembly 30 assembled to rotationally move on the base 11 of the HDD 10. The head is moved to a target position on the rotating hard disk 20 according to stewing of the magnetic head assembly 30.
The magnetic head assembly 30 includes a magnetic head slider 50 having the magnetic head attached that can write or read information on or from the hard disk 20 at one end thereof, an actuator arm 32 connected to a rotary axis 34 to allow rotation, and a suspension 31 connected between the actuator arm 32 and the magnetic head slider 50.
The magnetic head slider 50 is biased to the hard disk 20 by the suspension 31, and when the hard disk 20 starts to rotate, the magnetic head slider 50 flies and floats on a cushion of air over the hard disk 20 as a result of air flow pressure generated by the rotation of the hard disk 20. When the magnetic head slider 50 flies and floats, a gap between the magnetic head and the surface of the hard disk 20 that results is the flying height.
FIG. 2 is a perspective view of a typical magnetic head 70. Referring to FIG. 2, the magnetic head 70 includes a magneto-resistive head 74 for reproducing and an inductive write head for recording. The magneto-resistive head 74 senses and reads a magnetic signal recorded on the hard disk 20. The inductive write head writes a desired signal on the hard disk 20. The inductive write head includes a top pole 71 and a bottom pole 72, which are separated from each other by a predetermined gap to form a leakage flux for magnetizing a magnetic layer of the hard disk 20, and a write coil 73, which generates a magnetic field by applying a current thereto.
Recently, in HDDs, TPI (track per inch) has been increased to increase storage capacity, flying height has been reduced, and write frequency has increased.
To reduce a track width of the hard disk 20, a width of the inductive write head for writing a magnetic signal on the track should be reduced according to the reduction of the track width. To read a magnetic signal written on the narrowed track, the flying height of the magnetic head 70 should be lowered.
It is preferable that the flying height of the magnetic head 70 be as low as possible within an acceptable limitation. The flying height of the magnetic head 70 is optimized by considering the number of rotations of a spindle motor, a disk substance, and mechanical characteristics of the head assembly.
However, the flying height of the magnetic head 70 may vary due to an operational temperature of the HDD 10, atmospheric pressure, moisture content in the air, or a driving voltage of the HDD 10. For example, the atmospheric pressure in the HDD 10, which varies according to a user environment, influences air flow pressure required to float the magnetic head 70.
Thus, it is necessary to consider these variables, in order to optimize the flying height of the magnetic head 70.
The lower the flying height of the magnetic head 70, the less a margin of a head-disk interface (HDI). In particular, if the flying height is too high, a weak write may occur, and if the flying height is too low, the magnetic head 70 may crash onto the hard disk 20.
Methods of measuring a flying height of a head are disclosed in Japanese Patent Publication No. 2003-7017, Korean Patent Publication No. 2001-78765, U.S. Pat. No. 5,377,058, etc.
FIGS. 3A and 3B are illustrations for explaining thermal pole tip protrusion (TPTP). FIG. 3A illustrates a state when a reproducing operation is performed, and FIG. 3B illustrates a state when a recording operation is performed. The flying height (FH) is shown as the distance between the hard disk 20 and the head attached to the head slider 50. Referring to FIG. 3B, it is known that the top and bottom write poles 71 and 72 protrude (FH>FH′) when a recording operation is performed compared to when a reproducing operation is performed as illustrated in FIG. 3A. The protrusion of the write poles 71 and 72 occurs due to a heat expansion coefficient difference between the nonmetallic head slider 50 and the metallic head 70. The protrusion causes a reduction in the area between the hard disk 20 and the head, resulting in a new flying height (FH′). The amount of TPTP is proportional to I2R, wherein I denotes a write current and R denotes resistance of the write coil 73. In other words, the TPTP is an inevitable phenomenon occurring due to a current flowing through the write coil 73.
The TPTP influences the HDI. If the write poles 71 and 72 protrude due to the TPTP, the gap between the magnetic head 70 and the hard disk 20 is reduced (FH>FH′). Accordingly, the margin of the HDI is reduced.
FIG. 4 is a waveform diagram for explaining an effect of a crash between a head and a disk when a recording operation is performed. In FIG. 4, an A section on the left represents a time period during which the head does not crash onto the disk, and a B section on the right represents a time period during which the head periodically crashes onto the disk. It can be seen that a waveform of a reproducing signal has a periodic fluctuation in the B section. The periodic fluctuation is a result of the periodical crash between the head and the disk when the recording operation is performed in the B section. This phenomenon is called a modulation phenomenon, and it is observed that the higher the altitude, the more severe the modulation phenomenon. This is because the higher the altitude, the lower the atmospheric pressure, resulting in a lower flying height of the head, and thereby causing a worse effect due to the TPTP. Thus, it is preferable that write strength influencing the TPTP is controlled according to the flying height of the head.